U.S. patent application number 16/474822 was filed with the patent office on 2019-11-14 for hot-water-sterilized packaging and method for producing same.
This patent application is currently assigned to KURARAY CO., LTD.. The applicant listed for this patent is KURARAY CO., LTD.. Invention is credited to Rina HOSHIKA, Makoto OKAMOTO, Makoto SUZUKI.
Application Number | 20190345280 16/474822 |
Document ID | / |
Family ID | 62709505 |
Filed Date | 2019-11-14 |
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United States Patent
Application |
20190345280 |
Kind Code |
A1 |
HOSHIKA; Rina ; et
al. |
November 14, 2019 |
HOT-WATER-STERILIZED PACKAGING AND METHOD FOR PRODUCING SAME
Abstract
A hot-water sterilized package includes a container having a
barrier layer filled with contents, wherein the barrier layer
contains 96 mass % or more of a modified ethylene-vinyl alcohol
copolymer based on the resin total, the modified ethylene-vinyl
alcohol copolymer is represented by a following formula (I),
contents (mol %) of a, b, and c based on the total monomer units
satisfy following formulae (1) through (3), a degree of
saponification (DS) defined by a following formula (4) is 90 mol %
or more, and in measurement using a differential scanning
calorimeter (DSC), crystalline melting enthalpy (.DELTA.H.sub.A:
J/g) during temperature rise in a hydrated state and crystalline
melting enthalpy (.DELTA.H.sub.B: J/g) during temperature rise
after drying and melting followed by rapid cooling satisfy
following formulae (5) and (6). A container constituting such a
package has excellent in oxygen barrier properties even after
hot-water sterilization, and thus degradation of content quality is
inhibited for a long period. ##STR00001## 18.ltoreq.a.ltoreq.55 (1)
0.01.ltoreq.c.ltoreq.20 (2)
[100-(a+c)].times.0.9.ltoreq.b.ltoreq.[100-(a+c)] (3) DS=[(Total
Number of Moles of Hydrogen Atoms in X,Y, and Z)/(Total Number of
Moles of X,Y, and Z)].times.100 (4)
.DELTA.H.sub.A/.DELTA.H.sub.B.gtoreq.0.5 (5)
.DELTA.H.sub.B.gtoreq.70 (6).
Inventors: |
HOSHIKA; Rina;
(Kurashiki-shi, JP) ; OKAMOTO; Makoto;
(Kurashiki-shi, JP) ; SUZUKI; Makoto;
(Kurashiki-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KURARAY CO., LTD. |
Kurashiki-shi |
|
JP |
|
|
Assignee: |
KURARAY CO., LTD.
Kurashiki-shi
JP
|
Family ID: |
62709505 |
Appl. No.: |
16/474822 |
Filed: |
December 28, 2017 |
PCT Filed: |
December 28, 2017 |
PCT NO: |
PCT/JP2017/047335 |
371 Date: |
June 28, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61L 2/04 20130101; B65D
65/40 20130101; B32B 2250/246 20130101; B32B 2250/03 20130101; C08F
2800/10 20130101; A61L 2202/23 20130101; B32B 27/08 20130101; B32B
2439/00 20130101; C08F 216/38 20130101; A23L 3/10 20130101; C08L
29/04 20130101; B32B 27/306 20130101; B65B 55/10 20130101; B32B
27/32 20130101; B32B 2250/40 20130101; B32B 2307/7244 20130101;
B65B 55/02 20130101 |
International
Class: |
C08F 216/38 20060101
C08F216/38; A61L 2/04 20060101 A61L002/04; B32B 27/08 20060101
B32B027/08; B32B 27/30 20060101 B32B027/30; B32B 27/32 20060101
B32B027/32; B65D 65/40 20060101 B65D065/40; B65B 55/02 20060101
B65B055/02 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 29, 2016 |
JP |
2016-257385 |
Claims
1. A hot-water sterilized package, comprising a container filled
with contents, wherein the container comprises a barrier layer, the
barrier layer comprises 96 mass % or more of a modified
ethylene-vinyl alcohol copolymer based on a total amount of resin,
the modified ethylene-vinyl alcohol copolymer is represented by a
formula (I), contents (mol %) of a, b, and c based on the total
monomer units satisfy formulae (1) through (3), a degree of
saponification (DS) defined by a formula (4) is 90 mol % or more,
and in measurement using a differential scanning calorimeter (DSC),
crystalline melting enthalpy (.DELTA.H.sub.A: J/g) during
temperature rise in a hydrated state and crystalline melting
enthalpy (.DELTA.H.sub.B: J/g) during temperature rise after drying
and melting followed by rapid cooling satisfy formulae (5) and (6),
##STR00008## wherein in the formula (I), each of R.sup.1, R.sup.2,
R.sup.3, and R.sup.4 independently denotes a hydrogen atom or an
alkyl group having a carbon number from 1 to 10, and the alkyl
group may include a hydroxyl group, an alkoxy group, or a halogen
atom; and each of X, Y, and Z independently denotes a hydrogen
atom, a formyl group, or an alkanoyl group having a carbon number
from 2 to 10 18.ltoreq.a.ltoreq.55 (1) 0.01.ltoreq.c.ltoreq.20 (2)
[100-(a+c)].times.0.9.ltoreq.b.ltoreq.[100-(a+c)] (3) DS=[(Total
Number of Moles of Hydrogen Atoms in X,Y, and Z)/(Total Number of
Moles of X,Y, and Z)].times.100 (4)
.DELTA.H.sub.A/.DELTA.H.sub.B.gtoreq.0.5 (5) .DELTA.H.sub.B70
(6).
2. The package according to claim 1, wherein R.sup.1, R.sup.2,
R.sup.3, and R.sup.4 are hydrogen atoms.
3. The package according to claim 1, wherein each of X, Y, and Z is
independently a hydrogen atom or an acetyl group.
4. The package according to claim 1, wherein the container
comprises a multilayer structure having layers comprising any one
of polyolefin, polyamide, or polyester arranged on both sides of
the barrier layer.
5. A method of producing the package according to claim 1,
comprising: filling the container with the contents; and then
sterilizing the container with hot water.
Description
TECHNICAL FIELD
[0001] The present invention relates to a hot-water sterilized
package comprising a modified ethylene-vinyl alcohol copolymer and
a method of producing the same.
BACKGROUND ART
[0002] Ethylene-vinyl alcohol copolymers (hereinafter, may be
abbreviated as EVOH) are resins exhibiting excellent gas barrier
properties to odor, flavor, and the like and are preferably used
for packaging containers for foods and the like. Such a packaging
container is then filled with contents such as foods to form a
package, which may be heat treated with hot water or water vapor
for sterilization (hereinafter, may be abbreviated as hot-water
sterilization). Heat treatment of EVOH for a long time however
causes problems of resin whitening and deterioration in shape
retention performance for the vacuum packed contents.
[0003] Some techniques are reported to solve such problems. Patent
Documents 1 and 2 describe molded articles (films, sheets, etc.) of
resin compositions containing EVOH and polyimide (hereinafter, may
be abbreviated as PA). However, they have a problem of appearance
damage because a large amount of moisture permeates EVOH, probably
due to the hydrophilicity of EVOH, causing voids in the packaging
material and whitening.
[0004] As a material to solve the above problems, Patent Document 3
describes a resin composition containing PA and EVOH having
structural units derived from 1,3-diacetoxy-2-methylenepropane
(hereinafter, may be abbreviated as MPDAc). However, the resin
composition contains PA and thus has a problem of reduction in
barrier properties characteristic of EVOH.
[0005] For such reasons, a package is expected to have excellent
barrier properties and the barrier properties not to be reduced
even after hot-water sterilization.
PRIOR ART DOCUMENTS
Patent Documents
[0006] Patent Document 1 JP 2009-242591 A
[0007] Patent Document 2 WO 2015/174396
[0008] Patent Document 3 JP 2015-151428 A
SUMMARY OF THE INVENTION
Problems to be Solved by the Invention
[0009] The present invention has been made to solve the above
problems and is to provide a package including a container filled
with contents, excellent in oxygen barrier properties even after
hot-water sterilization without damaging the gas barrier properties
originally possessed by EVOH.
Means of Solving the Problems
[0010] The above problems are solved by providing a hot-water
sterilized package, comprising a container having a barrier layer
filled with contents, wherein the barrier layer contains 96 mass %
or more of modified EVOH based on the resin total, the modified
EVOH is represented by a following formula (I), contents (mol %) of
a, b, and c based on the total monomer units satisfy following
formulae (1) through (3), a degree of saponification (DS) defined
by a following formula (4) is 90 mol % or more, and in measurement
using a differential scanning calorimeter (DSC), crystalline
melting enthalpy (.DELTA.H.sub.A: J/g) during temperature rise in a
hydrated state and crystalline melting enthalpy (.DELTA.H.sub.B:
J/g) during temperature rise after drying and melting followed by
rapid cooling satisfy following formulae (5) and (6),
##STR00002##
[In the formula (I), each of R.sup.1, R.sup.2, R.sup.3, and R.sup.4
independently denotes a hydrogen atom or an alkyl group having a
carbon number from 1 to 10, and the alkyl group may include a
hydroxyl group, an alkoxy group, or a halogen atom. Each of X, Y,
and Z independently denotes a hydrogen atom, a formyl group, or an
alkanoyl group having a carbon number from 2 to 10.]
18.ltoreq.a.ltoreq.55 (1)
0.01.ltoreq.c.ltoreq.20 (2)
[100-(a+c)].times.0.9.ltoreq.b.ltoreq.[100-(a+c)] (3)
DS=[(Total Number of Moles of Hydrogen Atoms in X,Y, and Z)/(Total
Number of Moles of X,Y, and Z)].times.100 (4)
.DELTA.H.sub.A/.DELTA.H.sub.B.gtoreq.0.5 (5)
.DELTA.H.sub.B70 (6).
[0011] At this time, it is preferred that R.sup.1, R.sup.2,
R.sup.3, and R.sup.4 are hydrogen atoms. It is also preferred that
each of X, Y, and Z is independently a hydrogen atom or an acetyl
group.
[0012] It is preferred that the container is made of a multilayer
structure having layers containing any one of polyolefin,
polyimide, or polyester arranged on both sides of the barrier
layer.
[0013] The above problems are also solved by providing a method of
producing the package, comprising: filling the container with the
contents; and then sterilizing the container with hot water.
Effects of the Invention
[0014] The container constituting the package of the present
invention is excellent in oxygen barrier properties even after
hot-water sterilization to inhibit degradation of content quality
for a long period.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a .sup.1H-NMR spectrum of a modified EVAc obtained
in Example 1
[0016] FIG. 2 is a .sup.1H-NMR spectrum of a modified EVOH obtained
in Example 1
MODES FOR CARRYING OUT THE INVENTION
[0017] The present invention is a hot-water sterilized package,
comprising a container having a barrier layer filled with contents,
wherein
[0018] the barrier layer contains 96 mass % or more of modified
EVOH based on the resin total,
[0019] the modified EVOH is represented by a following formula (I),
contents (mol %) of a, b, and c based on the total monomer units
satisfy following formulae (1) through (3), a degree of
saponification (DS) defined by a following formula (4) is 90 mol %
or more, and in measurement using a differential scanning
calorimeter (DSC), crystalline melting enthalpy (.DELTA.H.sub.A:
J/g) during temperature rise in a hydrated state and crystalline
melting enthalpy (.DELTA.H.sub.B: J/g) during temperature rise
after drying and melting followed by rapid cooling satisfy
following formulae (5) and (6),
##STR00003##
[In the formula (I), each of R.sup.1, R.sup.2, R.sup.3, and R.sup.4
independently denotes a hydrogen atom or an alkyl group having a
carbon number from 1 to 10, and the alkyl group may include a
hydroxyl group, an alkoxy group, or a halogen atom. Each of X, Y,
and Z independently denotes a hydrogen atom, a formyl group, or an
alkanoyl group having a carbon number from 2 to 10.]
18.ltoreq.a.ltoreq.55 (1)
0.01.ltoreq.c.ltoreq.20 (2)
[100-(a+c)].times.0.9.ltoreq.b.ltoreq.[100-(a+c)] (3)
DS=[(Total Number of Moles of Hydrogen Atoms in X,Y, and Z)/(Total
Number of Moles of X,Y, and Z)].times.100 (4)
.DELTA.H.sub.A/.DELTA.H.sub.B.gtoreq.0.5 (5)
.DELTA.H.sub.B70 (6).
[Modified EVOH]
[0020] The modified EVOH used in the present invention is
represented by the above formula (I). The modified EVOH has, in
addition to ethylene units and vinyl alcohol units, monomer units
having a 1,3-diol structure in main chain of the copolymer and thus
the crystallinity decreases compared with EVOH not containing the
monomer units, so that it is possible to improve flexibility and
secondary processability. Moreover, with the modified EVOH, since
the 1,3-diol structure has strong hydrogen bonding strength, it is
possible to reduce a decrease in barrier property caused by
decrease in crystallinity.
[0021] In the above formula (I), each of R.sup.1, R.sup.2, R.sup.3,
and R.sup.4 independently denotes a hydrogen atom or an alkyl group
having a carbon number from 1 to 10, and the alkyl group may
include a hydroxyl group, an alkoxy group, or a halogen atom. Each
of X, Y, and Z independently denotes a hydrogen atom, a formyl
group, or an alkanoyl group having a carbon number from 2 to
10.
[0022] In the formula (I), R.sup.1, R.sup.2, R.sup.3, and R.sup.4
may be same groups and may also be different. The structure of the
alkyl group is not particularly limited and may have a branched
structure and a cyclic structure in part. In addition, the alkyl
group may include a hydroxyl group, an alkoxy group, or a halogen
atom. R.sup.1, R.sup.2, R.sup.3, and R.sup.4 are preferably a
hydrogen atom or an alkyl group having a carbon number from 1 to 5,
and more preferably a hydrogen atom. A preferred example of the
alkyl group may include a linear or branched alkyl group, such as a
methyl group, an ethyl group, an n-propyl group, an isopropyl
group, an n-butyl group, an isobutyl group, a tert-butyl group, and
a pentyl group, and among all, a methyl group and an ethyl group
are more preferred and a methyl group is even more preferred.
[0023] The formula (I) has a hydroxyl group in a case that X, Y, or
Z is a hydrogen atom, and the formula (I) has an ester group in a
case that X, Y, or Z is a formyl group or an alkanoyl group. The
alkanoyl group is preferably an alkanoyl group having a carbon
number from 2 to 5 and more preferably an acetyl group, a propanoyl
group, a butanoyl group, and the like, and even more preferably an
acetyl group. It is preferred that all of X, Y, and Z are a
hydrogen atom or a mixture containing a hydrogen atom.
[0024] Monomer units containing X is usually obtained by
saponifying vinyl ester. Accordingly, it is preferred that X is a
mixture of a hydrogen atom with a formyl group or an alkanoyl group
having a carbon number from 2 to 10. Considering availability of
the monomer (vinyl acetate) and production costs, it is more
preferred that X is a mixture of a hydrogen atom with an acetyl
group.
[0025] Meanwhile, it is possible to produce monomer units
containing Y and Z by copolymerizing unsaturated monomer units
having a 1,3-diester structure, followed by saponification, and it
is also possible to produce them by directly copolymerizing
unsaturated monomer units having a 1,3-diol structure. Accordingly,
both Y and Z may be a hydrogen atom only, or may be a mixture of a
hydrogen atom with a formyl group or an alkanoyl group having a
carbon number from 2 to 10, more preferably a mixture of a hydrogen
atom with an acetyl group.
[0026] In the modified EVOH, contents (mol %) of a, b, and c based
on the total monomer units satisfy following formulae (1) through
(3).
18.ltoreq.a.ltoreq.55 (1)
0.01.ltoreq.c.ltoreq.20 (2)
[100-(a+c)].times.0.9.ltoreq.b.ltoreq.[100-(a+c)] (3)
[0027] The character a denotes a content (mol %) of ethylene units
based on the total monomer units, which is from 18 to 55 mol %.
When the ethylene unit content is less than 18 mol %, melt
formability of the modified EVOH deteriorates. The character a is
preferably 22 mol % or more. In contrast, when the ethylene unit
content is more than 55 mol %, barrier properties of the modified
EVOH become insufficient. The character a is preferably 50 mol % or
less, more preferably 40 mol % or less, and even more preferably 35
mol % or less.
[0028] The character c denotes a content (mol %) of monomer units
containing Y and Z shown at the right edge of the formula (I) based
on the total monomer units, which is from 0.01 to 20 mol %. When c
is less than 0.01 mol %, flexibility, formability, and secondary
processability of the modified EVOH become insufficient. Moreover,
barrier properties after hot-water sterilization are reduced. The
character c is preferably 0.05 mol % or more, more preferably 0.1
mol % or more, and even more preferably 0.2 mol % or more. In
contrast, when c is more than 20 mol %, crystallinity extremely
decreases and thus barrier properties, in particular barrier
properties after hot-water sterilization, of the modified EVOH are
reduced. The character c is preferably 10 mol % or less and more
preferably 5 mol % or less. In order to have particularly excellent
barrier properties, c is preferably 2.5 mol % or less and more
preferably 1.5 mol % or less.
[0029] The character b denotes a content (mol %) of vinyl alcohol
units and vinyl ester units based on the total monomer units. This
satisfies the following formula (3).
[100-(a+c)].times.0.9.ltoreq.b.ltoreq.[100-(a+c)] (3)
[0030] That is, in the modified EVOH, 90% or more of the monomer
units other than the ethylene units and than the monomer units
containing Y and Z shown at the right edge of the formula (I) is
vinyl alcohol units or vinyl ester units. In a case that the
formula (3) is not satisfied, the gas barrier properties become
insufficient. It is preferred to satisfy the following formula (3')
and more preferred to satisfy the following formula (3'').
[100-(a+c)].times.0.95.ltoreq.b.ltoreq.[100-(a+c)] (3')
[100-(a+c)].times.0.98.ltoreq.b.ltoreq.[100-(a+c)] (3'')
[0031] The modified EVOH has a degree of saponification (DS)
defined by the following formula (4) of 90 mol % or more.
DS=[(Total Number of Moles of Hydrogen Atoms in X,Y, and Z)/(Total
Number of Moles of X,Y, and Z)].times.100 (4)
[0032] In this context, the "total number of moles of hydrogen
atoms in X, Y, and Z" indicates a number of moles of the hydroxyl
group, and the "total number of moles of X, Y, and Z" indicates a
total number of moles of the hydroxyl group and the ester group.
When the degree of saponification (DS) becomes less than 90 mol %,
sufficient barrier performance is not obtained and moreover thermal
stability of the modified EVOH becomes insufficient and gels and
aggregates are easily generated during melt molding. In addition,
thermal stability decreases and thus long-run formability during
high temperature molding is prone to decrease. The degree of
saponification (DS) is preferably 95 mol % or more, more preferably
98 mol % or more, and even more preferably 99 mol % or more. In
order to have barrier properties and thermal stability that are
particularly excellent, the degree of saponification (DS) is
preferably 99 mol % or more, more preferably 99.5 mol % or more,
and even more preferably 99.8 mol % or more.
[0033] It is possible to obtain the degree of saponification (DS)
by nuclear magnetic resonance (NMR). It is also possible to obtain
the contents of the monomer units represented by a, b, and c above
by NMR. In addition, the modified EVOH used in the present
invention is usually a random copolymer. It is possible to confirm
to be a random copolymer from NMR and results of melting point
measurement.
[0034] The method of producing the modified EVOH is not
particularly limited and examples of the method may include a
method, comprising: obtaining a modified ethylene-vinyl ester
copolymer represented by the following formula (IV) by radical
polymerization of ethylene, vinyl ester represented by the
following formula (II), and an unsaturated monomer represented by
the following formula (III); and then saponifying it.
##STR00004##
[0035] In the formula (II), R.sup.5 denotes a hydrogen atom or an
alkyl group having a carbon number from 1 to 9. The carbon number
of the alkyl group is preferably from 1 to 4. Vinyl ester
represented by the formula (II) is exemplified by vinyl formate,
vinyl acetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate,
vinyl pivalate, vinyl versatate, vinyl caproate, and the like. From
an economic perspective, vinyl acetate is particularly
preferred.
##STR00005##
[0036] In the formula (III), R.sup.1, R.sup.2, R.sup.3, and R.sup.4
are same as those in the formula (I). Each of R.sup.6 and R.sup.7
independently denotes a hydrogen atom or an alkyl group having a
carbon number from 1 to 9. The carbon number of the alkyl group is
preferably from 1 to 4. Examples of the unsaturated monomer
represented by the formula (III) may include
2-methylene-1,3-propanediol diacetate, 2-methylene-1,3-propanediol
dipropionate, 2-methylene-1,3-propanediol dibutyrate, and the like.
Among all, 2-methylene-1,3-propanediol diacetate is preferably used
in view of easy production. In a case of
2-methylene-1,3-propanediol diacetate, R.sup.1, R.sup.2, R.sup.3,
and R.sup.4 are hydrogen atoms and R.sup.6 and R.sup.7 are methyl
groups.
##STR00006##
[0037] In the formula (IV), R.sup.1, R.sup.2, R.sup.3, R.sup.4,
R.sup.5, R.sup.6, R.sup.7, a, b, and c are same as those in the
formulae (I) through (III). The modified ethylene-vinyl ester
copolymer thus obtained is then subjected to saponification.
[0038] In addition, instead of the unsaturated monomer represented
by the above formula (III), an unsaturated monomer represented by
the following formula (V) may be copolymerized, and in this case,
only the units derived from the unsaturated monomer represented by
the above formula (II) are saponified.
##STR00007##
[0039] In the formula (V), R.sup.1, R.sup.2, R.sup.3, and R.sup.4
are same as those in the formula (I). Examples of the unsaturated
monomer represented by the formula (V) may include
2-methylene-1,3-propanediol and 2-methylene-1,3-butanediol.
[0040] The unsaturated monomers represented by the formula (III)
and the formula (V) used in the present invention have high
copolymerization reactivity with vinyl ester monomers, so that
copolymerization reaction proceeds easily. Accordingly, it is easy
to increase an amount of modification and a degree of
polymerization of the modified ethylene-vinyl ester copolymer thus
obtained. In addition, an amount of the unreacted unsaturated
monomers remaining after polymerization is less even when the
polymerization reaction is stopped at a low conversion, so that it
is excellent in respect of environment and cost. The unsaturated
monomers represented by the formula (III) and the formula (V) are
more excellent at this point than other monomers, such as allyl
glycidyl ether and 3,4-diacetoxy-1-butene, having a functional
group in an allylic position and having only one carbon atom. In
this context, the unsaturated monomer represented by the formula
(III) has higher reactivity than the unsaturated monomer
represented by the formula (V).
[0041] The mode of polymerization for production of a modified
ethylene-vinyl ester copolymer by copolymerizing ethylene, vinyl
ester represented by the above formula (II), and the unsaturated
monomer represented by the above formula (III) or (V) may be any of
batch polymerization, semi-batch polymerization, continuous
polymerization, and semi-continuous polymerization.
[0042] In addition, as the method of polymerization, it is possible
to employ a known method, such as a bulk polymerization method, a
solution polymerization method, a suspension polymerization method,
and an emulsion polymerization method. A bulk polymerization method
or a solution polymerization method is usually employed, in which
polymerization proceeds without solvent or in a solvent, such as
alcohol. In a case of obtaining a modified ethylene-vinyl ester
copolymer with a high degree of polymerization, employment of an
emulsion polymerization method becomes an option.
[0043] Although a solvent used in a solution polymerization method
is not particularly limited, alcohol is used preferably, and lower
alcohols, such as methanol, ethanol, and propanol, for example, are
more preferably used. An amount of solvent in a polymerization
reaction liquid may be selected considering the intended viscosity
average degree of polymerization of the modified EVOH and chain
transfer of the solvent, and a mass ratio of the solvent to the
total monomers contained in the reaction liquid (solvent/total
monomers) is selected from a range from 0.01 to 10, preferably a
range from 0.05 to 3.
[0044] A polymerization initiator used for copolymerization of
ethylene, vinyl ester represented by the above formula (II), and
the unsaturated monomer represented by the above formula (III) or
(V) is selected in accordance with the method of polymerization
from known polymerization initiators, for example, an azo
initiator, a peroxide initiator, and a redox initiator. The azo
initiator may include, for example, 2,2'-azobisisobutyronitrile,
2,2'-azobis(2,4-dimethylvaleronitrile), and
2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile). The peroxide
initiator may include, for example, percarbonate compounds, such as
diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate,
and diethoxyethyl peroxydicarbonate; perester compounds, such as
t-butylperoxy neodecanoate, .alpha.-cumylperoxy neodecanoate, and
acetyl peroxide; acetylcyclohexylsulfonyl peroxide;
2,4,4-trimethylpentyl-2-peroxyphenoxyacetate; and the like.
Potassium persulfate, ammonium persulfate, hydrogen peroxide, and
the like may be used in combination with the above initiators. The
redox initiator is a polymerization initiator in which, for
example, the above peroxide initiators and a reducing agent, such
as sodium hydrogen sulfite, sodium hydrogen carbonate, tartaric
acid, L-ascorbic acid, and rongalite, are combined. An amount of
polymerization initiator is different depending on the
polymerization catalyst and thus is not determined unconditionally,
and it is adjusted in accordance with the polymerization rate. The
amount of polymerization initiator based on vinyl ester monomers is
preferably from 0.01 to 0.2 mol % and more preferably from 0.02 to
0.15 mol %. Although the polymerization temperature is not
particularly limited, it is appropriately from room temperature to
150.degree. C. approximately, and preferably not less than
40.degree. C. and not more than a boiling point of a solvent to be
used.
[0045] For copolymerization of ethylene, vinyl ester represented by
the above formula (II), and the unsaturated monomer represented by
the above formula (III) or (V), they may be copolymerized in the
presence of a chain transfer agent as long as not inhibiting the
effects of the present invention. The chain transfer agent may
include, for example, aldehydes, such as acetaldehyde and
propionaldehyde; ketones, such as acetone and methylethylketone;
mercaptans, such as 2-hydroxyethanethiol; and phosphinates, such as
sodium phosphinate monohydrate. Among all, aldehydes and ketones
are used preferably. Although an amount of adding the chain
transfer agent to the polymerization reaction liquid is determined
in accordance with the chain transfer constant of the chain
transfer agent and the intended degree of polymerization of the
modified ethylene-vinyl ester copolymer, it is preferably from 0.1
to 10 parts by mass based on 100 parts by mass of the vinyl ester
monomer in general.
[0046] It is possible to obtain the modified EVOH by saponifying
the modified ethylene-vinyl ester copolymer thus obtained. At this
time, the vinyl ester units in the copolymer are converted to vinyl
alcohol units. In addition, ester bonds derived from the
unsaturated monomer represented by the formula (III) are also
hydrolyzed at the same time to be converted to a 1,3-diol
structure. In such a manner, it is possible to hydrolyze different
kinds of ester group by one saponification reaction at the same
time.
[0047] It is possible to employ a known method for a method of
saponifying the modified ethylene-vinyl ester copolymer. The
saponification reaction is usually carried out in an alcohol or
hydrous alcohol solution. Alcohol preferably used at this time is
lower alcohol, such as methanol and ethanol, and more preferably
methanol. Alcohol or hydrous alcohol used for the saponification
reaction may contain another solvent, as long as the solvent is 40
mass % or less of its mass, such as acetone, methyl acetate, ethyl
acetate, and benzene. The catalyst used for the saponification is,
for example, alkali metal hydroxides, such as potassium hydroxide
and sodium hydroxide; alkali catalysts, such as sodium methylate;
and acid catalysts, such as mineral acid. Although the temperature
to carry out the saponification is not limited, it is preferably in
a range from 20.degree. C. to 120.degree. C. In a case that
gelatinous products precipitate as the saponification proceeds, it
is possible to obtain modified EVOH by grinding the products and
then washing and drying them.
[0048] The modified EVOH may contain a structural unit derived from
another ethylenic unsaturated monomer that is copolymerizable with
ethylene, vinyl ester represented by the above formula (II), and
the unsaturated monomer represented by the above formula (III) or
(V) as long as not inhibiting the effects of the present invention.
Such an ethylenic unsaturated monomer may include, for example,
.alpha.-olefins, such as propylene, n-butene, isobutylene, and
1-hexene; acrylic acid and salts thereof; unsaturated monomers
containing an acrylic ester group; methacrylic acid and salts
thereof; unsaturated monomers containing a methacrylic ester group;
acrylamide, N-methylacrylamide, N-ethylacrylamide,
N,N-dimethylacrylamide, diacetoneacrylamide, acrylamide propane
sulfonic acid and salts thereof, and acrylamidopropyl dimethylamine
and salts thereof (for example, quaternary salts); methacrylamide,
N-methylmethacrylamide, N-ethylmethacrylamide, methacrylamide
propane sulfonic acid and salts thereof, and methacrylamidopropyl
dimethylamine and salts thereof (for example, quaternary salts);
vinyl ethers, such as methyl vinyl ether, ethyl vinyl ether,
n-propyl vinyl ether, i-propyl vinyl ether, n-butyl vinyl ether,
i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether,
stearyl vinyl ether, and 2,3-diacetoxy-1-vinyloxypropane; vinyl
cyanides, such as acrylonitrile and methacrylonitrile; vinyl
halides, such as vinyl chloride and vinyl fluoride; vinylidene
halides, such as vinylidene chloride and vinylidene fluoride; allyl
compounds, such as allyl acetate, 2,3-diacetoxy-1-allyloxypropane,
and allyl chloride; unsaturated dicarboxylic acids, such as maleic
acid, itaconic acid, and fumaric acid, and salts thereof or esters
thereof; vinylsilane compounds, such as vinyltrimethoxysilane; and
isopropenyl acetates.
[0049] In the modified EVOH after hot-water sterilization of the
present invention, and in measurement using a differential scanning
calorimeter (DSC), crystalline melting enthalpy (.DELTA.H.sub.A:
J/g) during temperature rise in a hydrated state and crystalline
melting enthalpy (.DELTA.H.sub.B: J/g) during temperature rise
after drying and melting followed by rapid cooling have to satisfy
the following formulae (5) and (6).
.DELTA.H.sub.A/.DELTA.H.sub.B.gtoreq.0.5 (5)
.DELTA.H.sub.B.gtoreq.70 (6)
[0050] It is possible to obtain the crystalline melting enthalpy
(.DELTA.H.sub.A: J/g) by measuring modified EVOH in a hydrated
state taken from the barrier layer of the container after hot-water
sterilization using a differential scanning calorimeter (DSC) for a
peak area in a temperature range from the start to the end of
melting during the first temperature rise. Specifically, as
described in Examples below, DSC measurement with a hot-water
treatment history remained in the modified EVOH is regarded as
crystalline melting enthalpy measurement of the modified EVOH after
hot-water sterilization.
[0051] It is possible to obtain the crystalline melting enthalpy
(.DELTA.H.sub.B: J/g) by drying and melting and then rapidly
cooling modified EVOH taken from the barrier layer of the container
after hot-water sterilization using a differential scanning
calorimeter (DSC) to obtain a peak area in a temperature range from
the start to the end of melting during temperature rise after that.
Specifically, as described in Examples below, DSC measurement
without a hot-water treatment history in the modified EVOH allows
measurement of a value equivalent to the crystalline melting
enthalpy of the modified EVOH before hot-water sterilization. This
is because, in DSC measurement, hot-water sterilized modified EVOH
is subjected to melting by heating to cancel the influence of a
change in the crystal structure caused by the hot-water
sterilization.
[0052] The present inventors surprisingly found that modified EVOH
having a 1,3-diol structure after hot-water sterilization sometimes
has more improved barrier properties than that before the
sterilization. The present inventors further investigated
considering that the effects are partly caused by the crystal
structure of the modified EVOH and found that barrier properties
are markedly improved when modified EVOH after hot-water
sterilization satisfies the above formulae (5) and (6), and thus
completed the present invention.
[0053] When the container is a multilayer structure described
later, the barrier layer containing the modified EVOH may be peeled
off from the other layers to be used for measurement of DHA and
.DELTA.H.sub.B.
[0054] A preferred melt flow rate (MFR) (at 190.degree. C. under a
load of 2160 g) of the modified EVOH is from 0.1 to 30 g/10 min.,
more preferably from 0.3 to 25 g/10 min., and even more preferably
from 0.5 to 20 g/10 min. It is noted that when the melting point is
about or over 190.degree. C., the measurements are carried out
under a load of 2160 g at a plurality of temperatures not lower
than the melting point. The results are plotted, in a semilog
graph, with reciprocals of absolute temperatures as abscissa
against logarithms of MFRs as ordinate and the preferable MFR is
represented by an extrapolation to 190.degree. C.
[0055] The modified EVOH may be a mixture of the modified EVOH with
unmodified EVOH. Use of such a mixture allows cost reduction. A
mass ratio (modified EVOH/unmodified EVOH) of the modified EVOH to
the unmodified EVOH in the mixture is preferably from 1/9 to 9/1.
From the perspective of more markedly exhibiting the effects of the
present invention, the EVOH preferably does not contain unmodified
EVOH.
[0056] In a case that the modified EVOH is a mixture of two or more
different kinds of modified EVOH above or a mixture of the EVOH
with unmodified EVOH, average values calculated from a blend weight
ratio are used for the contents of the monomer units represented by
a, b, and c, the degree of saponification, the MFR, .DELTA.H.sub.A,
and .DELTA.H.sub.B.
[0057] It is preferred that an oxygen transmission rate of the
hot-water sterilized modified EVOH at 20.degree. C. and 85% RH is
100 cc20 .mu.m/m.sup.2dayatm or less. The oxygen transmission rate
is more preferably 10 cc20 .mu.m/m.sup.2dayatm or less, even more
preferably 5 cc20 .mu.m/m.sup.2dayatm or less, particularly
preferably 3 cc20 .mu.m/m.sup.2dayatm or less, and most preferably
2 cc20 .mu.m/m.sup.2dayatm or less.
[0058] From the perspective of barrier properties, the barrier
layer has to contain 96 mass % or more of the modified EVOH based
on the resin total in the barrier layer. The content of the
modified EVOH is preferably 98 mass % or more and more preferably
99 mass % or more. Even more preferably, the resin in the barrier
layer is substantially the modified EVOH only. The contents of
resins other than the modified EVOH are small, and the influence of
such resins in the DSC measurement of the modified EVOH is
extremely small and ignorable. Accordingly, even when the barrier
layer contains a resin other than the modified EVOH, it is possible
to obtain .DELTA.H.sub.A and .DELTA.H.sub.B by the method described
in Examples below.
[0059] The resin other than the modified EVOH contained in the
barrier layer is not particularly limited, and examples of the
resin may include thermoplastic resins, such as polyolefin,
polyamide, polyester, polystyrene, polyvinyl chloride, acrylic
resins, polyurethane, polycarbonate, and polyvinyl acetate.
[0060] As long as not inhibiting the effects of the present
invention, a resin composition containing additives other than
resins may be used as a material for the barrier layer. Examples of
the additives may include metal salts, heat stabilizers,
antioxidants, ultraviolet absorbers, plasticizers, antistatic
agents, lubricants, colorants, fillers, stabilizers, surfactants,
desiccants, crosslinkers, fiber reinforcements, and the like. The
contents of such other additives in the resin composition is
preferably 30 mass % or less, more preferably 20 mass % or less,
even more preferably 10 mass % or less, and particularly preferably
5 mass % or less.
[0061] Among all, it is preferred to contain alkali metal salt as
the metal salt. By making a resin composition containing alkali
metal salt in such a manner, interlayer adhesion when laminated to
a resin other than the modified EVOH becomes even better. Although
cationic species of the alkali metal salt is not particularly
limited, it is preferably sodium salt or and potassium salt.
Anionic species of the alkali metal salt is also not particularly
limited. It is possible to add as salt of carboxylic acid, salt of
carbonic acid, salt of hydrogencarbonic acid, salt of phosphoric
acid, salt of hydrogenphosphoric acid, salt of boric acid,
hydroxide, and the like. It is preferred that an alkali metal salt
content in the resin composition is from 10 to 500 ppm in terms of
alkali metal elements. The interlayer adhesion is sometimes not
obtained sufficiently in a case that the alkali metal salt content
is less than 10 ppm, and it is more preferably 50 ppm or more. In
contrast, the melt stability is sometimes insufficient in a case
that the alkali metal salt content is more than 500 ppm, and it is
more preferably 300 ppm or less.
[0062] It is also preferred to contain a boron compound as the heat
stabilizer. By making a resin composition containing a boron
compound in such a manner, it is possible to suppress torque
variation during melting by heating. The boron compound used in the
present invention is not particularly limited and may include boric
acids, borate esters, salts of boric acids, boron hydrides, and the
like. Specifically, the boric acids may include orthoboric acid,
metaboric acid, tetraboric acid, and the like; the borate esters
may include triethyl borate, trimethyl borate, and the like; the
salts of boric acids may include alkali metal salts and alkaline
earth metal salts of various boric acids mentioned above, borax,
and the like. Among these compounds, orthoboric acid (hereinafter,
may be described simply as boric acid) is preferred. It is
preferred that the boron compound content in the resin composition
is preferably from 20 to not more than 2000 ppm in terms of boron
elements. The suppression of torque variation during melting by
heating sometimes becomes insufficient in a case that the boron
compound content is less than 20 ppm, and it is more preferably 50
ppm or more. In contrast, in a case that the boron compound content
is more than 2000 ppm, gelation easily occurs and the formability
sometimes deteriorates, and it is more preferably 1000 ppm or
less.
[0063] Moreover, it is also preferred to contain a phosphoric acid
compound as the heat stabilizer. By making a resin composition
containing a phosphoric acid compound in such a manner, it is
possible to prevent coloration during melt molding. The phosphoric
acid compound used in the present invention is not particularly
limited, and it is possible to use various acids, such as
phosphoric acid and phosphorous acid, and salts thereof. Although
the salt of phosphoric acid may be contained in any form of primary
phosphate, secondary phosphate, and tertiary phosphate, primary
phosphate is preferred. Although its cationic species is also not
particularly limited, alkali metal salt is preferred. Among them,
sodium dihydrogen phosphate and potassium dihydrogen phosphate are
preferred. It is preferred that the phosphoric acid compound
content in the resin composition is preferably from 5 to 200 ppm in
terms of phosphate radicals. The coloration resistance during melt
molding sometimes becomes insufficient in a case that the
phosphoric acid compound content is less than 5 ppm. In contrast,
the melt stability is sometimes insufficient in a case that the
phosphoric acid compound content is more than 200 ppm, and it is
more preferably 160 ppm or less.
[0064] Specific examples of other components may include the
following.
[0065] Antioxidant: 2,5-di-t-butyl-hydroquinone,
2,6-di-t-butyl-p-cresol, 4,4'-thiobis-(6-t-butylphenol),
2,2'-methylene-bis-(4-methyl-6-t-butylphenol),
octadecyl-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate,
4,4'-thiobis-(6-t-butylphenol), and the like.
[0066] Ultraviolet absorber:
ethylene-2-cyano-3',3'-diphenylacrylate,
2-(2'-hydroxy-5'-methylphenyl)benzotriazole,
2-(2'-hydroxy-3'-t-butyl-5'-methylphenyl) 5-chlorobenzotriazole,
2-hydroxy-4-methoxybenzophenone,
2,2'-dihydroxy-4-methoxybenzophenone, and the like.
[0067] Plasticizer: dimethyl phthalate, diethyl phthalate, dioctyl
phthalate, wax, liquid paraffin, phosphates, and the like.
[0068] Antistatic agent: pentaerythritol monostearate, sorbitan
monopalmitate, sulfated polyolefins, polyethylene oxide, Carbowax,
and the like.
[0069] Lubricant: ethylene bisstearoamide, butyl stearate, and the
like.
[0070] Colorant: carbon black, phthalocyanine, quinacridon,
indoline, azo pigments, red oxide, and the like.
[0071] Filler: glass fiber, vallastonite, calcium silicate, and the
like.
[0072] From the perspective of barrier properties, the content of
the modified EVOH in the resin composition is preferably 70 mass %
or more, and the modified EVOH is more preferably contained 80 mass
% or more, even more preferably 90 mass % or more, and particularly
preferably 95 mass % or more.
[0073] A method of containing such other components in the modified
EVOH is not particularly limited and a known method is
employed.
[Container]
[0074] Although the container used in the present invention may be
made of a single layer structure having the barrier layer only, it
is preferably made of a multilayer structure having the barrier
layer and other layers from the perspective of functional
improvement. The material constituting such other layers may
include thermoplastic resins other than the modified EVOH. A
container made of a multilayer structure having a modified EVOH
layer and layers of another thermoplastic resin other than the
modified EVOH layer is more suitable for hot-water
sterilization.
[0075] Examples of the resin used to form the layers of another
thermoplastic resin may include:
[0076] high density, medium density, and low density
polyethylene;
[0077] polyethylene produced by copolymerizing vinyl acetate,
acrylic ester, or .alpha.-olefin, such as butene and hexene;
[0078] ionomer resins;
[0079] polypropylene homopolymers;
[0080] polypropylene produced by copolymerizing .alpha.-olefin,
such as ethylene, butene, and hexene;
[0081] modified polypropylene with a rubber-based polymer blended
therein;
[0082] polyolefin, such as resins with maleic anhydride added or
grafted to these resins; polyamide; polyester; polystyrene;
polyvinyl chloride; acrylic resins; polyurethane; polycarbonate;
polyvinyl acetate; and the like. Among them, polyolefin, polyamide,
and polyester are preferred.
[0083] Each layer of the multilayer structure may be laminated via
an adhesive resin layer. The adhesive resin used for the adhesive
resin layer may include acid-modified polyolefin and the like.
Examples of the acid-modified polyolefin may include olefin-based
polymers having unsaturated carboxylic acid or a derivative thereof
introduced by chemical bonding and the like.
[0084] Layer configuration of the multilayer structure is not
particularly limited, and from the perspective of formability,
costs, and the like, representative examples may include another
thermoplastic resin layer/modified EVOH layer/another thermoplastic
resin layer, modified EVOH layer/adhesive resin layer/another
thermoplastic resin layer, another thermoplastic resin
layer/adhesive resin layer/modified EVOH layer/another
thermoplastic resin layer, another thermoplastic resin
layer/adhesive resin layer/modified EVOH layer/adhesive resin
layer/another thermoplastic resin layer, and the like. Preferred
layer configurations of the multilayer structure are another
thermoplastic resin layer/modified EVOH layer/another thermoplastic
resin layer, another thermoplastic resin layer/adhesive resin
layer/modified EVOH layer/another thermoplastic resin layer, and
another thermoplastic resin layer/adhesive resin layer/modified
EVOH layer/adhesive resin layer/another thermoplastic resin layer.
To provide layers of another thermoplastic resin as both outer
layers of the modified EVOH layer, the layers of another
thermoplastic resin as both outer layers may be layers of different
resins or may be layers of the same resin. Among all, the container
is preferably made of a multilayer structure having layers
containing any one of polyolefin, polyamide, or polyester arranged
on both sides of the barrier layer.
[0085] Examples of the method of producing the multilayer structure
used as the container may include, but not particularly limited to,
coextrusion lamination, coextrusion molding, extrusion lamination,
dry lamination, extrusion blow molding, coextrusion blow molding,
coinjection molding, solution coating, and the like. Among them,
coextrusion lamination and coextrusion molding are preferred, and
coextrusion molding is more preferred. Lamination of the modified
EVOH layer to the layer of another thermoplastic resin by the above
methods allows easy and reliable production of the multilayer
structure. The multilayer structure is obtained as a sheet or a
film by the above methods, and examples of the method of molding
the sheet or the film thus obtained may include vacuum molding,
pressure molding, vacuum-pressure molding, blow molding, and the
like. Such molding is usually carried out in a temperature range of
not more than the melting point of EVOH.
[Hot-Water Sterilized Package]
[0086] The package of the present invention is a hot-water
sterilized package, comprising the container filled with contents.
Examples of the contents to fill the container may include, but not
particularly limited to, foods, beverages, medical products, and
the like.
[0087] The hot-water sterilization herein means sterilization from
60.degree. C. to 140.degree. C. in the presence of moisture, and
specific examples may include retorting and boiling. Examples of
the method of exposing the package to moisture may include a method
comprising contacting with vapor, a method comprising immersing in
hot water, a method comprising showering the package with hot
water, and the like. The hot-water sterilized package herein means
a package to which the above sterilization is applied.
[0088] Retorting is a method of sterilizing microorganisms, such as
mold, yeast, and bacteria, by heat under pressure to store foods
and the like. In general, a package having a container filled with
foods and the like, where the container has an intermediate layer
of a gas barrier resin, is sterilized under pressure under
conditions from 105.degree. C. to 140.degree. C., from 0.15 to 0.3
MPa, and from 5 to 120 min. There are retort systems of a steam
type using heated steam, a hot-water immersion type using
pressurized superheated water, and the like to be appropriately
used in accordance with sterilization conditions of the contents,
such as foods.
[0089] Boiling is a sterilization method with hot water to store
foods and the like. In general, while the conditions may differ
depending on the contents, a package having a container filled with
foods and the like, where the container has an intermediate layer
of a gas barrier resin, is sterilized under conditions from
60.degree. C. to 100.degree. C., at an atmospheric pressure, and
from 10 to 120 min. Boiling is usually carried out using a hot
water chamber, which includes a batch type for immersion in the hot
water chamber at a constant temperature to be taken out after a
certain time and a continuous type for sterilization by putting
through the hot water chamber like a tunnel.
[0090] It is possible to produce the package of the present
invention by filling the container with the contents, followed by
the hot-water sterilization.
[0091] Since the hot-water sterilized package of the present
invention is excellent in gas barrier properties, quality
degradation of contents, such as foods and medical products, is
inhibited for a long period.
EXAMPLES
[0092] Although further detailed descriptions are given below to
the present invention by Examples, the present invention is not
limited to Examples.
Production Example 1
(1) Synthesis of Modified EVAc
[0093] To a 250 L pressure reaction vessel provided with a jacket,
a stirrer, a nitrogen inlet, an ethylene inlet, and an initiator
addition port, 120 kg of vinyl acetate (R.sup.5 is a methyl group
in the formula (II): hereinafter, referred to as VAc), 18 kg of
methanol (hereinafter, may be referred to as MeOH), and 0.9 kg of
2-methylene-1,3-propanediol diacetate (R.sup.1, R.sup.2, R.sup.3,
and R.sup.4 are hydrogen atoms and R.sup.6 and R.sup.7 are methyl
groups in the formula (III): hereinafter, referred to as MPDAc)
were charged, and the temperature was raised to 60.degree. C., and
after that, nitrogen bubbling was carried out for 30 minutes to
purge inside the reaction vessel with nitrogen. Subsequently,
ethylene was introduced to have a reaction vessel pressure
(ethylene pressure) of 3.4 MPa. After the temperature in the
reaction vessel is adjusted at 60.degree. C., 36 g of
2,2'-azobis(2,4-dimethylvaleronitrile) ("V-65" produced by Wako
Pure Chemical Industries, Ltd.) as an initiator was added in the
form of methanol solution to initiate polymerization. During the
polymerization, the ethylene pressure was maintained at 3.4 MPa and
the polymerization temperature at 60.degree. C. After 6 hours, when
the conversion of VAc became 45%, the polymerization was stopped by
cooling. After removing ethylene by opening the reaction vessel, a
nitrogen gas was bubbled to completely remove ethylene.
Subsequently, after unreacted VAc was removed under reduced
pressure, MeOH was added to the modified ethylene-vinyl acetate
copolymer (hereinafter, may be referred to as modified EVAc) to
which a structural unit derived from MPDAc was introduced by
copolymerization to have a 20 mass % MeOH solution.
(2) Saponification of Modified EVAc
[0094] To a 500 L reaction vessel provided with a jacket, a
stirrer, a nitrogen inlet, a reflux condenser, and a solution
addition port, a 20 mass % MeOH solution of the modified EVAc
obtained in (1) was charged. The temperature was raised to
60.degree. C. while blowing nitrogen into the solution, and 0.5
equivalents of sodium hydroxide with respect to vinyl acetate units
in the modified EVAc was added in the form of MeOH solution of 2 N.
After completion of adding the MeOH sodium hydroxide solution,
saponification reaction proceeded by stirring for 2 hours while
keeping the temperature in the system at 60.degree. C. After that,
acetic acid was added to stop the saponification reaction. After
that, while heating and stirring from 60.degree. C. to 80.degree.
C., ion exchange water was added to drain MeOH outside the reaction
vessel and to precipitate modified EVOH. The precipitated modified
EVOH was collected and ground with a mixer. The modified EVOH
powder thus obtained was added in a 1 g/L aqueous acetic acid
solution (bath ratio of 20:proportion of 1 kg of the powder to 20 L
of the aqueous solution) and it was stirred and washed for 2 hours.
It was deliquored and was further put into a 1 g/L aqueous acetic
acid solution (bath ratio of 20) and it was stirred and washed for
two hours. An operation of putting one obtained by deliquoring it
into ion exchange water (bath ratio of 20) for stirring and washing
for 2 hours and deliquoring it was repeated three times to carry
out purification. Subsequently, it was stirred and immersed in 10 L
of an aqueous solution containing 0.5 g/L of acetic acid and 0.1
g/L of sodium acetate for 4 hours and then deliquored, and it was
dried at 60.degree. C. for 16 hours to obtain roughly dried
modified EVOH. The modified EVOH thus obtained had a melt flow rate
(MFR) (at 190.degree. C. under a load of 2160 g) of 1.5 g/10
min.
(3) Production of Modified EVOH Hydrous Pellet
[0095] To a 80 L stirring vessel provided with a jacket, a stirrer,
and a reflux condenser, the roughly dried modified EVOH obtained in
(2), water, and MeOH were charged and the temperature was raised to
80.degree. C. for dissolution. The solution was extruded in a
liquid mixture of water/MeOH=90/10 cooled at 5.degree. C. through a
tube having a diameter of 4 mm to be precipitated in the form of
strand, and the strand was cut with a strand cutter into pellets to
obtain modified EVOH hydrous pellets. The moisture content of the
modified EVOH hydrous pellets thus obtained was measured by a
halogen moisture meter "HR 73" manufactured by Mettler and it was
60 mass %.
(4) Production of Modified EVOH Composition Pellet
[0096] In a 1 g/L aqueous acetic acid solution (bath ratio of 20),
the modified EVOH hydrous pellets obtained in (3) above was added
and it was stirred and washed for 2 hours. It was deliquored and
was further added in a 1 g/L aqueous acetic acid solution (bath
ratio of 20) and it was stirred and washed for 2 hours. After
deliquoring, the aqueous acetic acid solution was renewed and same
operation was carried out. An operation of putting one, obtained by
washing with the aqueous acetic acid solution and then deliquoring
it, into ion exchange water (bath ratio of 20) for stirring and
washing for 2 hours and deliquoring it was repeated 3 times to
carry out purification, and thus modified EVOH hydrous pellets from
which the catalyst residue during the saponification reaction was
removed were obtained. The hydrous pellets were added in an aqueous
solution (bath ratio of 20) having a sodium acetate concentration
of 0.5 g/L, an acetic acid concentration of 0.8 g/L, and a
phosphoric acid concentration of 0.005 g/L for immersion for 4
hours while periodically stirred. They were deliquored and dried at
80.degree. C. for 3 hours and at 105.degree. C. for 16 hours,
thereby obtaining modified EVOH composition pellets.
(5) Content of Each Structural Unit in Modified EVAc
[0097] In the modified EVAc, the content of ethylene units (a mol %
in the formula (IV)), the content of structural units derived from
vinyl acetate (b mol % in the formula (IV)), and the content of
structural units derived from MPDAc (c mol % in the formula (IV))
were calculated by .sup.1H-NMR measurement of the modified EVAc
before saponification.
[0098] Firstly, a small amount of the MeOH solution of modified
EVAc obtained in (1) was sampled and modified EVAc was precipitated
in ion exchange water. The precipitate was collected and dried at
60.degree. C. under vacuum, and thus dried modified EVAc was
obtained. Next, the dried modified EVAc thus obtained was dissolved
in dimethyl sulfoxide (DMSO)-d6 containing tetramethylsilane as the
internal standard material and measured at 80.degree. C. using 500
MHz .sup.1H-NMR ("GX-500" manufactured by JEOL Ltd.).
[0099] FIG. 1 illustrates, as a .sup.1H-NMR spectrum of modified
EVAc, a spectrum of the modified EVAc obtained in Example 1. Each
peak in the spectrum is assigned as follows:
[0100] from 0.6 to 1.0 ppm: methylene proton (4H) in a terminal
region of ethylene unit;
[0101] from 1.0 to 1.85 ppm: methylene proton (4H) in an
intermediate region of ethylene unit, methylene proton (2H) in main
chain of structural unit derived from MPDAc, methylene proton (2H)
of vinyl acetate unit;
[0102] from 1.85 to 2.1 ppm: methyl proton (6H) of structural unit
derived from MPDAc and methyl proton (3H) of vinyl acetate
unit;
[0103] from 3.7 to 4.1 ppm: methylene proton (4H) in side chain of
structural unit derived from MPDAc;
[0104] from 4.4 to 5.3 ppm: methine proton (1H) of vinyl acetate
unit.
[0105] In accordance with the above assignment, where the integral
value from 0.6 to 1.0 ppm is x, the integral value from 1.0 to 1.85
ppm is y, the integral value from 3.7 to 4.1 ppm is z, and the
integral value from 4.4 to 5.3 ppm is w, the ethylene unit content
(a: mol %), the vinyl ester unit content (b: mol %), and the
content of structural units derived from MPDAc (c: mol %) are
calculated according to the following formulae, respectively.
a=(2x+2y-z-4w)/(2x+2y+z+4w).times.100
b=8w/(2x+2y+z+4w).times.100
c=2z/(2x+2y+z+4w).times.100
[0106] As a result of calculating in the above method, the ethylene
unit content (a) was 27.0 mol %, the vinyl ester unit content (b)
was 72.5 mol %, the content (c) of structural units derived from
MPDAc was 0.5 mol %. The values of a, b, and c in the modified EVAc
were same as the values of a, b, and c in the modified EVOH after
saponification.
(6) Degree of Saponification of Modified EVOH
[0107] The modified EVOH after saponification was also subjected to
.sup.1H-NMR measurement similarly. The roughly dried modified EVOH
obtained in (2) above was dissolved in dimethyl sulfoxide (DMSO)-d6
containing tetramethylsilane as the internal standard material and
tetrafluoroacetic acid (TFA) as an additive and measured at
80.degree. C. using 500 MHz .sup.1H-NMR ("GX-500" manufactured by
JEOL Ltd.). FIG. 2 illustrates, as an example of a .sup.1H-NMR
spectrum of modified EVOH, a spectrum of the modified EVOH obtained
in Example 1. Since the peak intensity from 1.85 to 2.1 ppm
decreased drastically, it is clear that the ester group contained
in the structural units derived from MPDAc, in addition to the
ester group contained in vinyl acetate, was also saponified to be
hydroxyl group. From the .sup.1H-NMR spectrum obtained in Example 1
as well, such a decrease of the peak intensity from 1.85 to 2.1 ppm
was observed. The degree of saponification was calculated from the
peak intensity ratio of the methyl proton of vinyl acetate unit
(from 1.85 to 2.1 ppm) and the methine proton of vinyl alcohol unit
(from 3.15 to 4.15 ppm). The degree of saponification of the
modified EVOH in Example 1 was 99.9 mol % or more.
(7) Melting Point of Modified EVOH
[0108] Measurement of the modified EVOH composition pellets
obtained in (4) above was performed according to JIS K7121 by
raising the temperature from 30.degree. C. to 215.degree. C. at a
rate of 10.degree. C./min., and after that, rapidly cooling it to
-35.degree. C. at 100.degree. C./min., and again from -35.degree.
C. to 195.degree. C. at a rate of temperature rise of 10.degree.
C./min. (differential scanning calorimeter (DSC) "RDC220/SSC5200H"
manufactured by Seiko Instruments & Electronics Ltd.). For
temperature calibration, indium and lead were used. The peak
melting temperature (Tpm) was obtained from the 2nd-run chart in
accordance with the JIS above to define it as the melting point of
modified EVOH. The melting point was 187.degree. C.
(8) Sodium Salt Content and Phosphoric Acid Compound Content in
Modified EVOH Composition
[0109] In a teflon (registered trademark) pressure vessel, 0.5 g of
the modified EVOH composition pellets obtained in (4) above was
placed and 5 mL of concentrated nitric acid was added there for
decomposition at room temperature for 30 minutes. After 30 minutes,
the lid was closed for decomposition by heating at 150.degree. C.
for 10 minutes and subsequently at 180.degree. C. for 5 minutes
with a wet digestion apparatus ("MWS-2" manufactured by Actac
Corp.), and after that, it was cooled to room temperature. The
process liquid was poured into a 50 mL measuring flask (made of
TPX) and diluted with pure water. With this solution, analysis of
contained metal was carried out by an ICP emission
spectrophotometer ("OPTIMA4300DV" manufactured by Perkin-Elmer
Inc.) and the contents of sodium elements and phosphorus elements
were obtained. The sodium salt content was 150 ppm in terms of
sodium elements, and the phosphoric acid compound content was 10
ppm in terms of phosphate radicals.
Production Examples 2 Through 14
[0110] Modified EVAc, modified EVOH, and modified EVOH composition
pellets were prepared and analyzed in the same manner as that in
Production Example 1 except for changing the polymerization
conditions in Production Example 1 (1) as shown in Table 1. The
results are shown in Table 1.
TABLE-US-00001 TABLE 1 Modified EVOH Polymerization Condition
Degree of Initial Charge Polymer- Polymer- Saponi- Vinyl Ethylene
ization ization Final a c fication Acetate Methanol Modifier
Pressure Initiator Temperature Time Conversion Content Content (DS)
kg kg Type .sup.1) kg MPa g .degree. C. hours % mol % mol % mol %
Production 120 18 1 0.9 3.4 36 60 6 45 27 0.5 .gtoreq.99.9 Example
1 Production 120 12 1 1.9 3.5 48 60 6 48 27 1.0 .gtoreq.99.9
Example 2 Production 120 12 1 2.7 3.5 48 60 6.5 48 27 1.5
.gtoreq.99.9 Example 3 Production 110 11 1 0.8 4.1 44 60 4.5 40 32
0.5 .gtoreq.99.9 Example 4 Production 110 8 1 1.7 4.2 44 60 4.5 40
32 1 .gtoreq.99.9 Example 5 Production 100 10 1 1 4.9 44 60 6 45 38
0.5 .gtoreq.99.9 Example 6 Production 90 9 1 0.4 5.7 72 60 6 40 44
0.2 .gtoreq.99.9 Example 7 Production 100 30 None -- 2.9 15 60 6 46
27 -- .gtoreq.99.9 Example 8 Production 100 30 None -- 3.7 20 60 4
44 32 -- .gtoreq.99.9 Example 9 Production 90 27 None -- 4.5 18 60
6 48 38 -- .gtoreq.99.9 Example 10 Production 110 6 1 2.4 4.3 44 60
6 40 32 1.4 .gtoreq.99.9 Example 11 Production 110 2 1 6.2 4.3 88
60 7 35 32 3.9 .gtoreq.99.9 Example 12 Production 120 12 1 4.9 3.5
48 60 6 32 27 3.0 .gtoreq.99.9 Example 13 Production 90 9 1 1.9 5.8
72 60 6 60 44 1.4 .gtoreq.99.9 Example 14 .sup.1) Modifier 1:
2-methylene-1,3-propanediol diacetate
Example 1
(1) Preparation of Multilayer Sheet
[0111] The modified EVOH composition pellets obtained in Production
Example 1 was used as a material and formed into a film to have
3-layer configuration of polypropylene layer/modified EVOH
composition layer/polypropylene layer using a 2-type 3-layer
coextruder to prepare a multilayer sheet. At this point, each
polypropylene layer had a thickness of 360 .mu.m and the modified
EVOH layer had a thickness of 80 .mu.m. The multilayer sheet thus
obtained was cut into A4 size, heat sealed on three sides, fed with
500 mL of distilled water inside, and heat sealed on the remained
side to obtain a package before hot-water sterilization. The
package before hot-water sterilization was immersed in hot water at
120.degree. C. for 30 minutes for hot-water sterilization (hot
water immersion) to obtain a hot-water sterilized package.
(2) Measurement of .DELTA.H.sub.A and .DELTA.H.sub.B
[0112] Using a differential scanning calorimeter (DSC) "Q2000"
manufactured by TA Instruments Inc., .DELTA.H.sub.A and
.DELTA.H.sub.B were obtained by DSC measurement in accordance with
JIS K7121. For temperature calibration, indium was used. The
preparation method and the measurement procedure of a sample used
in each measurement were as follows. The results are shown in Table
1.
(2-1) Measurement of .DELTA.H.sub.A
[0113] From the package after hot-water sterilization, an
approximately 2 mg section in terms of modified EVOH was cut.
Further, from the section, the polypropylene layers as the inner
and outer layers were delaminated to obtain a section of the
modified EVOH layer. The total amount of the section thus obtained
was sealed in a hermetic pan (manufactured by TA Instruments Inc.)
and subjected to DSC measurement by raising the temperature from
30.degree. C. to 241.degree. C. at a rate of 10.degree. C./min. The
crystalline melting enthalpy (.DELTA.H.sub.A: J/g) was obtained by
a peak area in a temperature range from the start to the end of
melting during the first temperature rise in the DSC curve thus
obtained. In the present measurement, the hermetic pan was used to
prevent evaporation of water vapor during the measurement.
(2-2) Measurement of .DELTA.H.sub.B
[0114] From the package after hot-water sterilization, an
approximately 2 mg section in terms of modified EVOH was cut.
Further, from the section, the polypropylene layers as the inner
and outer layers were delaminated to obtain a section of the
modified EVOH layer. The total amount of the section thus obtained
was sealed in an aluminum pan (manufactured by TA Instruments Inc.)
and subjected to DSC measurement by raising the temperature from
30.degree. C. to 241.degree. C. at a rate of 10.degree. C./min.,
followed by rapid cooling to 92.degree. C. at 10.degree. C./min.,
and again temperature rise from 92.degree. C. to 241.degree. C. at
a rate of 10.degree. C./min. The crystalline melting enthalpy
(.DELTA.H.sub.B: J/g) was obtained by a peak area in a temperature
range from the start to the end of melting during the second
temperature rise in the DSC curve thus obtained.
(3) Measurement of Oxygen Transmission Rate of Package before
Hot-Water Sterilization
[0115] A sheet prepared by cut opening the package before hot-water
sterilization thus obtained was moisture conditioned for 2 months
in the conditions of 20.degree. C. and inner layer 100% RH/outer
layer 65% RH to be served for measurement of the oxygen
transmission rate in the same conditions ("OX-TORAN MODEL 2/21"
manufactured by MOCON, Inc.). The results are shown in Table 2.
TABLE-US-00002 TABLE 2 Modified EVOH Degree of Oxygen Transmission
Rate .sup.2) Difference Saponification Before After in Oxygen
Production a Content c Content (DS) .DELTA.H.sub.A/ .DELTA.H.sub.B
Hot-Water Hot-Water Transmission Example mol % Modifier .sup.1) mol
% mol % .DELTA.H.sub.B (J/g) Sterilization Sterilization Rate
.sup.2) Example 1 1 27 1 0.5 .gtoreq.99.9 0.55 78 1.4 0.6 0.8
Example 2 2 27 1 1.0 .gtoreq.99.9 0.53 74 2.2 1 1.2 Example 3 3 27
1 1.5 .gtoreq.99.9 0.52 70 2.6 1.3 1.3 Example 4 4 32 1 0.5
.gtoreq.99.9 0.57 76 1.8 0.9 0.9 Example 5 5 32 1 1.0 .gtoreq.99.9
0.55 73 2.4 1.6 0.8 Example 6 6 38 1 0.5 .gtoreq.99.9 0.66 74 3.4
2.2 1.2 Example 7 7 44 1 0.2 .gtoreq.99.9 0.63 75 5.3 4 1.3
Comparative 8 27 unmodified -- .gtoreq.99.9 0.56 84 1.3 1.6 -0.3
Example 1 Comparative 9 32 unmodified -- .gtoreq.99.9 0.58 82 2 2.3
-0.3 Example 2 Comparative 10 38 unmodified -- .gtoreq.99.9 0.59 77
3.3 3.7 -0.4 Example 3 Comparative 11 32 1 1.4 .gtoreq.99.9 0.48 70
2.7 3 -0.3 Example 4 Comparative 12 32 1 3.9 .gtoreq.99.9 0.4 36 4
4.3 -0.3 Example 5 Comparative 13 27 1 3.0 .gtoreq.99.9 0.4 49 3.5
4.4 -0.9 Example 6 Comparative 14 44 1 1.0 .gtoreq.99.9 0.57 65 5
5.5 -0.5 Example 7 .sup.1) modifier 1: 2-methylene-1,3-propanediol
diacetate .sup.2) unit: cc 20 .mu.m/m.sup.2 day atm
(4) Measurement of Oxygen Transmission Rate of Package after
Hot-Water Sterilization
[0116] A sheet prepared by cut opening the package after hot-water
sterilization was moisture conditioned for 2 months in the
conditions of 20.degree. C. and inner layer 100% RH/outer layer 65%
RH to be served for measurement of the oxygen transmission rate in
the same conditions ("OX-TORAN MODEL 2/21" manufactured by MOCON,
Inc.). The results are shown in Table 2.
Examples 2 Through 7, Comparative Examples 1 Through 7
[0117] A package was prepared and evaluated in the same manner as
that in Example 1 except for changing the type of EVOH (EVOH
composition) as shown in Table 1. The results are shown in Table
2.
[0118] The hot-water sterilized packages of the present invention
(Examples 1 through 7) of the modified EVOH with monomer units
having a 1,3-diol structure were excellent in oxygen barrier
properties after hot-water sterilization. In contrast, the cases of
using unmodified EVOH (Comparative Examples 1 through 3) and using
modified EVOH not satisfying .DELTA.H.sub.A and .DELTA.H.sub.B
defined in the present invention (Comparative Examples 4 through 7)
had lower oxygen barrier properties after hot-water
sterilization.
* * * * *